Ur S4/S6 ignition problem

2.2 I5 20v turbo - 230bhp
4.2 V8 32v Naturally Aspirated - 326bhp
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AndyH-R6S
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Joined: Sun Mar 26, 2006 7:58 pm
Location: Welling

Ur S4/S6 ignition problem

Post by AndyH-R6S » Mon Feb 26, 2007 10:53 am

Has any body had this particular problem with there standard or modified Ur S6/S4?

While driving on a motorway, and accelerating moderate to hard, the engine hesitates for a few seconds (Max) and then accelerates OK but maybe with a very slight roughish feel to the power, then other times using the exactly the same driving technique the car accelerates off smoothly and with plenty if vigour from the start. (Normal) It tends to only happen in top gear (between 60 to 100mph) but some times I have witnessed the event in the gear below.

The car has been fully checked over by an Audi specialist but nothing can be found. The only potential issue might be that the intercooler is too small for the engine conversion. However, when the external temperature is 4°C externally and exact same driving technique is used and the event does not occur, I would doubt that the intercooler is the issue. My past experience with turbo cars has suggested potential poor ignition/fuel delivery. Possible spark plug/lead or coil pack breakdown may be?

The car has a ‘MTM’ engine conversion so it is running higher boost than normal but this phenomenon occurs as the boost is starting to build up at around ‘0.8 to 1.2 bar’ and the ever so slight. Throttle position tends to make very little difference but I have noticed on the very odd occasions that using a slightly smaller throttle opening works better but there is still a very slight roughish feel to the power.

Lastly and totally not connected, has any body seen more than ‘2.2 to 2.3’ bar indicated on the internal instrument display panel? As mine should indicate more pressure after the MTM conversion but it might be the case that the display is not capable of going any higher? (The engine boost has been seen to go higher on calibrated boost gauge)

Any thoughts out there as when it goes on the rolling road it never does it?

Ba,

Andy H.

gn3dr
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Post by gn3dr » Mon Mar 05, 2007 10:00 am

Haven't had that prob myself but from what I have read it could be as you say, one of the coils breaking down. (They are supposed to be changed at 120K miles I believe)
Also a possible boost leak might be worth investigating.
I've never seen more than 2.0 bar on my gauge... but my car is standard.

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AndyH-R6S
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Location: Welling

Post by AndyH-R6S » Mon Aug 27, 2007 8:17 pm

The miss-fire saga is now solved, although the bits to repair are probably going to cost nearly a thousand pounds or so fix.

Took the ignition coil carrier off the top of the engine and found each coil pack cable, cracked at the point of entry to the coil pack and cracks to the cables at the rear of the top cover, not to mention three slightly loose spark plugs with oil round there bases. (Slight loss of compression but spark plug colour OK, Last time I trust the service agent!!!)

All cleaned up nicely with brand new plugs fitted. Not happy with the ‘Audi’ Prices for the coil pack/leads and the ‘POS’ blocks. I am investigating a replacement set, “AAN High Output coil kit” from ‘www.034motorsport’ that does away with all the old parts. Should also look neater as well, I hope. The cracks in the cables are due to heat and age and are almost invisible to the eye but a very close inspection showed various splits/cracks in the cable covering where the copper cable strands can be seen.

Only started out replacing the blown turbo output hose and having a general clean up, now replacing all sorts of bits but it will be worth it. (I will post the pictures of the converted spark plug coil pack arrangement in a few weeks.)

Splits in the coil leads are highlighted in yellow.

Bits being replaced:

All five coil packs, spark plugs and leads. (Ouch!!!)
Discarding both of the ‘POS’ amplifiers if I fit the ‘034 MS’ kit.
Vacuum hoses at the back of the engine, as they are nice and crunchy. (Above exhaust area)
Turbo output hose to Intercooler transfer tube. (Samco)
Transfer tube to Intercooler hose. (Samco)
Intercooler to Plenum hose. (Samco)
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